1. Field of the Invention
The present invention relates to a toner composition used, for example, as dry toner for developing an electrostatic latent image.
2. Description of Related Art
A toner using a binder resin as the major component and containing a pigment, a charge controlling agent, an external additive or the like has conventionally been used as a toner for a printer employing an electrostatic latent image developing system.
For example, in a printer employing an electrostatic latent image developing system as shown in FIG. 5, this type of toner T may be fed off from a tank 1 by a supply roller 2. After a toner layer formed on a developing roller 3 is made uniform by a blade 7, the toner T is applied to the surface of a photoconductor 4.
The surface of the photoconductor 4 is charged so as to correspond to a certain image pattern by a laser scanner unit 5 and a corona unit 6, while the toner T is charged to a polarity opposite to that on the surface of the photoconductor 4. The toner T is therefore attracted onto a portion charged on the photoconductor 4, but not to portions which are not charged. Namely, the toner T is dispersed so as to correspond to the certain image pattern (charge pattern) on the surface of the photoconductor 4.
A medium 9 such as paper or the like is then pressed against the photoconductor 4 via an image transfer roller 8 so that the toner image may be transferred onto the medium 9. Heat is then applied to the toner T by a fusing roller 10 so that it is melted and fused on the surface of the medium, thus accomplishing printing of the image.
To ensure printing of high image quality using the aforementioned method, it is necessary to prevent a fog (a symptom noted on the surface of a photoconductor and a recording medium in which toner sticks to a location to which it should not stick) and a blur (a symptom noted on a printed medium in which breaks of toner occur).
To prevent a fog, toner must be sufficiently charged so that an attraction force (a Coulomb force) acting between the toner and a charged portion on a surface of the photoconductor (to which toner is supposed to stick) becomes strong.
It is also necessary to make the level of charge of toner uniform, thereby minimizing a ratio of part of toner that is not sufficiently charged or that is charged to an opposite polarity.
It has therefore been conventionally practiced that a charge controlling agent and an external additive are added to the toner to increase the level of charge of toner and that a conductive titanium oxide is used as the external additive to make the level of charge of toner uniform.
To prevent a blur, on the other hand, an adequate amount of toner must be supplied smoothly to different components of the printer (e.g., the supply roller, the developing roller, and the photoconductor).
To accomplish it, it is necessary to increase fluidity of toner so as not to allow toner particles to be coagulated easily. To do that, it has been conventionally practiced that a hydrophobic silica is externally added to the toner.
Increasing the level of charge of toner by adding a charge controlling agent or an external additive and making the level of charge uniform by adding a conductive titanium oxide have not been sufficient to ensure high print image quality.
That is, even with these measures taken, there are left toner particles that are not sufficiently charged or toner particles that are charged to an opposite polarity (faultily charged toner particles) among the toner particles charged. The faultily charged toner particles are attracted by a Coulomb force and accumulated onto the surface of the developing roller. From the surface of the developing roller, the faultily charged toner particles are transferred to the surface of the photoconductor, thus sticking to a portion on the surface of the photoconductor, to which they are not supposed to stick, resulting at times in a fog.
Especially when running a continuous durability print cycle to print large numbers of pages, the level of charge of toner as a whole gradually drops to increase the number of faultily charged toner particles as the printer turns out more printed pages. This significantly increases the amount of faultily charged toner particles piled up on the surface of the developing roller, thus aggravating the fog problem.
Another problem that has conventionally been common is that a hydrophobic silica or other substance that is externally added to enhance fluidity of toner is separated from the toner and sticks to the photoconductor and a recording medium and the external additive prevents toner from sticking to the photoconductor and the recording medium, resulting in a blur on the printed image.
In view of the foregoing, it is therefore an object of the invention to provide a toner composition that ensures printing of clear-cut images of high quality without producing a fog or a blur.
To achieve the foregoing object, a toner composition according to one aspect of the invention has a shape of a particle containing a binder resin, and a surface of the toner composition is coated with an external additive comprising a hydrophobic silica and a conductive titanium oxide and, at the same time, the particle making up the toner composition has an average particle diameter by volume of 7 xcexcm or less and an external additive coating ratio of 70% or less and a coagulation level indicating the degree with which each of toner particles making up the toner composition is coagulated each other is 10% or less.
 less than 1 greater than  Effect of Preventing a Fog
i) A particle making up the toner composition according to the invention (hereinafter referred to as the toner particle) has a small average particle diameter by volume of 7 xcexcm or less, which results in a high ratio of a surface area of the toner particle to a weight thereof. This makes it possible to inject a larger amount of the charge controlling agent to the surface of the toner particle with respect to the weight thereof, allowing the level of the charge per unit weight of the toner particle to be made high.
Since the surface of the toner composition according to the invention is covered with the conductive titanium oxide, a charge can be transferred by way of the conductive titanium oxide between toner particles, contributing to smaller variations in the level of charge among different toner particles.
In, for example, a printer that employs a system of charging toner particles by letting a blade and toner particles on a surface of a developing roller rub together as shown in FIG. 5, it is difficult to allow all toner particles to be in uniform contact with the blade, which tends to cause variations in the level of charge to become greater among different toner particles, which is particularly true when the toner particles become small. Thanks to the effect of the conductive titanium oxide, the toner composition according to the invention allows toner particles to be uniformly charged.
Namely, in the toner composition according to the invention, the average particle diameter by volume of the toner particle is made small and, at the same time, the surface of the toner composition is covered with the conductive titanium oxide. This allows the level of charge per unit weight of the toner composition to be higher and, at the same time, the distribution of the level of charge to be narrower.
When the toner composition according to the invention is charged, there are contained very little toner particles that are not sufficiently charged or toner particles that are charged to an opposite polarity, and there is no chance of faultily charged toner particles being accumulated on, for example, the developing roller. A fog is not, therefore, likely to result from the toner composition according to the intention.
Particularly when printing a large number of pages continuously (in a continuous durability print cycle), the charge controlling agent and the external additive made of hydrophobic silica may gradually separate from the toner particle or they may be embedded inside the toner particle, causing the level of charge of the toner particle being gradually decreased Even in such a case, the toner composition according to the invention has a high level of charge per unit weight and a narrow distribution of the level of charge in the beginning, it is less likely that faultily charged toner particles are produced and therefore there is less chance of faultily charged toner particles being accumulated on the developing roller.
ii) The toner composition according to the invention has a characteristic that, because of the conductive titanium oxide contained therein, a fluidity thereof does not drop even when it is subjected to a repetitive mechanical force by a roller of the printer or the like during, for example, a continuous durability print cycle.
Therefore, since an amount more than necessary of the toner composition according to the invention supported by the developing roller is easily scraped off by, for example, the photoconductor or the supply roller, there is no possibility that an amount of toner composition more than a predetermined one is accumulated on the developing roller, which contributes to an even smaller likelihood that a fog occurs.
iii) As described earlier, the toner composition according to the invention has a high level of charge per unit weight and a narrow distribution of the level of charge. This allows the toner particles to be distributed accurately on, for example, the surface of the photoconductor of the printer, corresponding to a charged pattern on the surface of the photoconductor, thus reducing the chance of producing a fogs
That is, since the toner composition according to the invention has a high level of charge per unit weight, the attraction force (a Coulomb force) acting between the toner particle and a portion on the surface of the photoconductor that is charged (to which toner is supposed to stick) is sufficiently stronger than the attraction force (e.g., a van der Waals attraction) acting between the toner particle and a portion on the surface of the photoconductor that is not charged (to which toner should not stick). Toner particles are therefore selectively attracted onto the charged portion on the surface of the photoconductor. Moreover, since the distribution of the level of charge among different toner particles is narrow (that is, the ratio of faultily charged toner particles remains low), only a small amount of toner particles stick to the non-charged portion on the surface of the photoconductor.
It is preferable that the average particle diameter by volume of the toner composition range, for example, between 1 and 7 xcexcm. Making the average particle diameter by volume of the toner composition to 1 xcexcm or more, a toner spill inside the printer can be prevented, eliminating the possibility of spilled toner composition""s contaminating a printed medium.
 less than 2 greater than  Effect of Preventing a Blur
i) Since the external additive coating ratio of the toner composition according to the invention is 70% or less, there is sufficient room on the surface of the toner particle for applying an external additive and a large part of the external additive is present being stuck to the surface of the toner particle and there is only a very little of the external additive present away and free therefrom.
In the toner composition according to the invention, therefore, there is no chance that the external additive away and free from the toner particle sticks to, for example, the surface of the photoconductor or a recording medium (e.g., paper, OHP transparencies), thereby impeding the toner composition from sticking to the surface of the photoconductor or the recording medium, which contributes to a less chance of a blur.
It is preferable that the external additive coating ratio range between, for example, 5 and 70%. By making the external additive coating ratio to a value of 5% or more, it becomes possible, for example, to stably replenish the supply of toner composition, allowing a uniform toner layer to be formed. This, in turn, results in a blur being prevented.
ii) Since the toner composition according to the invention contains a hydrophobic silica as the external additive, it offers a high fluidity and is not easy to coagulate (coagulation level of 10% or less).
Moreover, only an adequate amount of the toner composition according to the invention is supplied smoothly to, for example, different components of the printer (e.g., the supply roller, the developing roller, and the photoconductor), which helps prevent a blur from occurring.
It is preferable that the coagulation level of the toner composition range between 1 and 10%. By making the coagulation level to a value of 1% or more, fluidity of the toner composition does not become excessively high, which helps prevent, for example, a toner spill inside the printer. This eliminates the possibility of spilled toner composition""s contaminating a printed medium.
 less than 3 greater than  Effect from Being Capable of Printing to a High Resolution
Since the toner composition according to the invention has an average particle diameter by volume of 7 xcexcm or less, it can be applied to printing requiring a high resolution
The toner composition according to the invention may contain components, for example, a dye, pigment, organic finely divided powder, charge controlling agent or the like, in addition to the binder resin.
Typical types of hydrophobic silica include silica subjected to surface treatment using dimethyldichlorosilane, dimethyl polysiloxane, hexamethyldisilazine, amino-silane, and amine, or the like. Commercially available silica products include, for example, H2000, H3004, HVK2150, or the like manufactured by Wacker Co., Ltd. and R974, RY200, RX200, RX300, RA200H, REA200, or the like manufactured by Nippon Aerosil Co., Ltd.
As the conductive titanium oxide, it is preferable that titanium oxide having undergone surface treatment using tin oxide-based semiconductor or indium oxide-based semiconductor be used. It is particularly preferable that the conductive titanium oxide have a resistance value of about 1 to 50 xcexa9xc2x7cm and a BET area/weight ratio of about 5 to 70 m2/g. Example commercially available products include EC-100, EC-210, EC-300, EC-500 or the like manufactured by Titan Kogyo Kabushiki Kaisha.
The external additive coating ratio refers to the ratio of a portion covered with the external additive to the entire surface area of the toner composition. The external additive coating ratio may be calculated, for example, using the following equation, where S (m2/g) is a BET area/weight ratio of the external additive, R (xcexcm) is an average particle diameter by quantity, xcfx81 (g/cm3) is a true specific gravity of the toner composition, and P (%) is the amount of external additive applied.
External additive coating ratio (%)=(Sxc3x97Rxc3x97xcfx81xc3x97P)/24
The coagulation level is an index indicating the degree with which each of toner particles making up the toner composition is coagulated each other and may be calculated, for example, as follows.
A coarse mesh (e.g., a mesh having a sieve opening of 75 xcexcm), an intermediate mesh (e.g., a mesh having a sieve opening of 45 xcexcm), and a fine mesh (e.g., a mesh having a sieve opening of 20 xcexcm) are mounted in the upper step, middle step, and the lower step, respectively, of a powder tester (e.g., model PT-E powder tester manufactured by Hosokawa Micron Corporation) and a sample weighing W g (e.g., 10 g) is placed on the mesh in the upper step.
The test setup is then vibrated with a predetermined amplitude (e.g., an amplitude causing the amplitude scale to be 1 mm) for a predetermined period of time (e.g., 30 sec.). Then, weight Wa of the sample left on the upper step mesh, weight Wb of the sample left on the middle step mesh, and weight Wc of the sample left on the lower step mesh are measured and the measured values are substituted for the corresponding terms in the equations below to find the coagulation level.
A=(Wa/W)xc3x97100 
B=(Wb/W)xc3x97100xc3x97(3/5) 
C=(Wc/W)xc3x97100xc3x97(1/5) 
Coagulation level (%)=A+B+C 
The toner composition according to the invention is unique, wherein the toner composition contains a dye.
The toner composition according to the invention contains a dye and the toner composition can be of many different colors depending on the color of the dye to be included therein.
Furthermore, since the toner composition according to the invention develops a color by means of the dye, it is superior in color development performance and color reproduction to conventional toner compositions that develop colors with pigments.
Typical dyes to be used include a direct dye, acid dye, disperse dye, cationic dye, reactive dye, sulfur dye, oil-soluble dye, and a metallic complex dye. Particularly preferable are the disperse dye and the cationic dye.
Of the disperse dyes, typical black dyes include, for example, Kayalon Polyester Black EX-SF300, Kayalon Polyester Black BR-SF, Kayalon Polyester Black AUL-E, Kayalon Polyester Black AUL-S, and Kayalon Polyester Black ECX 300 manufactured by Nippon Kayaku Co., Ltd.; Resolin Black BSN 200% 01 manufactured by Bayer; Teratop Black RLA and Terasil Black SRL-01 200% manufactured by Ciba Specialty Chemicals; and, Dianix Black RS-E01, Dianix Black S-LF 01, Dianix Black HG-FS conc., Dianix Black TA-N 200% 01, Dianix Black RB-FS 200, Dianix Black RN-SE01, Dianix Black BG-PS 200% 01, Dianix Black SPH extra conc.liquid, Dianix Tuxedo Black F conc.liquid, Dianix Tuxedo Black H conc.liquid 01, Dianix Black K-B, Dianix Black E-G, Dianix Black S-LF 01, Dianix Black TA-N 200% 01, Dianix Black BG-FS 200% 01, and Dianix Black H conc.liquid 01 manufactured by Dyestar.
Typical yellow dyes include, for example, Kayalon Microester Yellow DX-LS, Kayalon Microester Yellow AQ-LE, Kayalon Polyester Light Yellow 5G-S, Kayalon Polyester Yellow 4G-E, Kayalon Polyester Yellow AN-SE, and Kayacelon Yellow E-HGL manufactured by Nippon Kayaku Co., Ltd.; Terasil Yellow 4G, Teratop Yellow NFG and Terasil Yellow GWL-01 150% manufactured by Ciba Specialty Chemicals; and, Dianix Yellow AC-E, Dianix Yellow F3G-E conc., Dianix Yellow 3G-E conc., Dianix Yellow H2G-FS, Dianix Yellow N-TAN, Dianix Yellow G-FS 200, DianixYellow UN-SE200new, Dianix Yellow SE-5G, Dianix Yellow K-4G, Dianix Yellow S-6G, Dianix Yellow AM-42, Dianix Yellow 7GL 200%, Dianix Yellow S-4C, Dianix Brilliant Yellow 5G-E, Dianix Yellow SE-G, Dianix Yellow SPH, Dianix Yellow UN-SE 200% new, Dianix Brilliant Yellow 10G, and Dianix YellowAN-FS liquid manufactured by Dyestar.
Typical magenta dyes include, for example, Kayalon Microester Red DX-LS, Xayalon Microester Red AQ-LE, Kayalon Polyester Red BL-E, Kayalon Polyester Red HL-SF, Kayalon Polyester Red AUL-S, Kayalon Polyester Red 3BL-S 200, Kayalon Polyester Red HBL-SF, Kayacelon Red E-2BL, and Kayalon PolyesterRubine 3GL-S150 manufactured by Nippon Kayaku Co., Ltd.; Teratop Red NFR, Teratop Pink 2GLA and Teratop Pink 3G manufactured by Ciba Specialty Chemicals; and, Dianix Rubine S-2G, Dianix Red SE-3B, Dianix Red BLS 200%, Dianix Red S-LF, Dianix Brilliant Red B-FS, Dianix Red AC-E, Dianix Red BN-SE, Dianix Red A2B-FS, Dianix Carmine UN-SE, Dianix Red CB-SE200, Dianix Red KB-SE, Dianix Red FB-E200, Dianix Red S-G, Dianix Red K-3G, Dianix Red E-FB, Dianix Red UN-SE, Dianix Red N-TAN, Dianix Red F2B 400%, and Dianix Pink FRL-SE 200 manufactured by Dyestar.
Typical cyan dyes include, for example, Kayalon Microester Blue DX-LS, Kayalon Microester Blue AQ-LE, Kayalon Polyester Blue T-S, Kayalon Polyester Turquoise Blue GL-S 200, Kayalon Polyester Light Blue BGL-S 200, Kayacelon Blue E-BG, Kayalon Polyester Blue BR-SF, Xayalon Polyester Blue AUL-S, Kayalon Polyester Blue 4G-S, Kayalon Polyester Brilliant Blue FR-S, and Kayalon Polyester Turquoise Blue GL-S(C)200 manufactured by Nippon Rayaku Co., Ltd.; Teratop Blue BGE, Terasil Blue 3RL-02 150%, Terasil blue BGE-01 200%, Terasil Blue BG-02 200%, and Terasil Blue X-BGE liquid manufactured by Ciba Specialty Chemicals; and, Dianix Turquoise Blue B-FS 200, Dianix Turquoise Blue G-FS 200, Dianix Turquoise Blue G-FS, Dianix Blue K-2G, Dianix Blue HF-2G, DianixBlue BBLSN 200%, Dianix Blue S-BB, Dianix Blue FBL 150%, Dianix Turquoise BN-FS 200%, Dianix Turquoise Blue B-FS 200, Dianix Blue K-2G, Dianix Blue S-BB, Dianix Blue K-FBL, Dianix Blue HF-2G, Dianix Blue S-2G, DianixBlue FR, Dianix Blue AC-E, Dianix Blue 3RLS, Dianix Blue FBL-E, DianixBlue GRN-E 200 01, Dianix Blue FBL 150%, Dianix Blue SPH, Dianix Blue N-TAN, Dianix Blue UN-SE, Dianix Blue S-BG, Dianix Blue KBN-FS, Dianix Blue KRN-FS, Dianix Blue BBLSN 200%, Dianix Turquoise S-BG, and Dianix Royal Blue SE-R manufactured by Dyestar.
To give an example of a method of manufacturing a toner composition containing a dye, as disclosed in Japanese Patent Application Laid-Open Publication No. HEI 10-326029, the dye and resin particles are dispersed in an aqueous solvent and the solvent is agitated, while being heated to a temperature that can range between a softening temperature of the resin particles and a temperature 40xc2x0 C. higher than the softening temperature. After the resin particles are colored with the dye, they are subjected to reduction cleaning in order to remove excess dye that deposits on the surface of the resin particles. For a solvent used in this reduction cleaning, an aqueous solvent in which sodium hydroxide or hydroxy sulfite is dissolved is to be used.
The toner composition according to the invention has a high fluidity for its spherical shape and a low void ratio for its high bulk density, which makes it superior in that it has a small heat loss during fusing.
The shape of the toner composition according to the invention may be represented by, for example, a sphericity (circularity) ranging between 1 and 0.95.
The sphericity (circularity) as the term used in this specification is one that, for example, is calculated through the following formula and the value is 1 if the shape is a true sphere. For measurement of sphericity, a flow type particle image analyzer FPIA-1000 manufactured by Sysmex may, for example, be used.
Sphericity (circularity)=L1/L2
Where,
L1: circumference of a circle having the same projection plane area as the particle image
L2: Length of outline of the particle projected image
The toner composition according to the invention is used as dry toner for electrostatic latent image developing.
Since it is less likely that a fog or blur occurs when the toner composition according to the invention is used, the toner composition according to the invention is right for dry toner for electrostatic latent image developing.
Furthermore, since the average particle diameter by volume of the toner composition according to the invention is 7 xcexcm or less, the toner composition according to the intention permits printing of high resolution.
An organic finely divided powder and a charge controlling agent may be added to the toner composition according to the invention in order to make it easy to charge. As a method of applying such a substance, the resin particles, and the organic finely divided powder and charge controlling agent are mixed together by means of a mechanical impact force, thereby injecting the organic finely divided powder and charge controlling agent into the surface of the resin particles, as disclosed, for example, in Japanese Patent Application Laid-Open Publication No. HEI 11-65164.
Typical organic finely divided powders added to achieve the foregoing purpose include an acrylic resin finely divided powder, a fluorinated resin finely divided powder, a silicone resin finely divided powder, and a melamine resin finely divided powder.
Typical charge controlling agents include a metallic azo compound, a salicylic metal complex, a nigrosine, a triphenylmethane, and grade 4 ammonium salt.
The toner composition according to the invention is characterized by that the particle comprising the binder resin is manufactured using a dispersion polymerization method.
The toner composition according to the invention is characterized by that the binder resin particle as a component of the toner composition is manufactured using the dispersion polymerization method.
Since the binder resin particle made using the dispersion polymerization method has a small average particle diameter and a narrow particle diameter distribution, the toner composition according to the invention can have a small particle diameter and a narrow particle diameter distribution.
Use of the toner composition according to the invention, therefore, makes possible printing of high resolution.
Moreover, since the toner composition according to the invention is manufactured using the dispersion polymerization method, it is easy to shape it into a sphere.
The dispersion polymerization method refers, for example, to the following. Namely, a monomer, a dispersing agent, initiator, and the like are loaded in a solvent and, when the solvent is set into a predetermined condition (e.g., a predetermined temperature), the initiator is made into a radical by which the monomer is polymerized to produce polymerized particles. At this time, a spot at which polymerization takes place is uniformly distributed throughout the solvent and a polymerization rate is constant regardless of the spot of polymerization thanks to an effect of the dispersing agent, which ensures that a large number of spherical polymerized particles of a uniform size are produced.
The above and further objects and novel features of the invention will more fully appear from following detailed description when the same is read in connection with the accompanying drawings. It is to be expressly understood, however, that the drawings are for the purpose of illustration only and not intended as a definition of the limits of the invention.